to me, shadowgast's pining doesn't fully kick in until after canon. now hold your tomatoes back for a minute & let me explain; we have got to take into account their personal journeys for this, we have to fully understand, unbiasedly, who and where they were at during canon. like, obviously it would be foolish to say that there wasn't some longing, chemistry, tension, a possibility there, it'd be a disservice to deny it; they click the second they meet but who they are is so far removed from who they have to be for it mean something good it'd be laughable if it weren't so deeply sad.
sure, they meet, they click, and then they try their damn hardest to spin it in a way that won't end up burning their hands. there is so much going on during canon, there's so much going on with them personally, there was no time for pining; the pull was there, there just wasn't time to dwell on it or nurture it in a way that wouldn't be determent to themselves.
but then they get to go home. they get to make their own home and that's when the realization hits, not unexpectedly but not weightless either, Oh, they want to build their home with the other. Oh, they want to live with the other. Oh.
and that's when the pining and longing and yearning and craving and lament fully sets in, because of course it takes them a While to get there, of course they agonizingly pin for each other for months, they're caleb fucking widogast and essek goddamn thelyss, they're damaged self-sabotaging self-hating dumbass wizards and healing happens in layers and is never ever linear and of course shadowgast pins, of course they're a slow burn, it just takes time to get there.